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Do some checking on this site.. This has been talked about many times..

It is important to take deltaT's, low side pressure, high side pressure, liquid line temp, suction line temp, and compressor amp checks on every unit you service and install.. As when all the data is collected it will tell you many thing that may or may not be operating properly..

For a piston system.. Proper charging..Superheat most important!
Take a wet bulb temp at the main return air grille or in return air duct..Take a deltaT across the indoor coil.. Take outdoor temp by the outdoor coil(not in direct sunlight)... Take a suction and liquid line pressure reading... Take a suction line temp 6-8inches from compressor or near the pump down valve and take a liquid line temp... Subtract boiling temp of the suction pressure from the suction line temp for the current superheat reading... This should line up to the superheat slide chart that takes into account the indoor wet bulb and out door temperature.... Note.. The indoor and outdoor coil must be clean and blower must be moving the required air before superheat is properly set...DUH!!
Now remember you took all reading on the system because to get a overall picture what the whole system is doing to make appropriate repairs..DUH!!

For a TXV... Proper charging.... Subcool is the most important.. You should know this and I am tired of typing..
Look it up in for your interest section..

As I stated it is most important for you to set the superheat on a piston metered system and subcool on a TXV system but that does not mean that you don't need to take other reading to get an overall picture of the internal operation of the freon..

Goodluck
J

Please change your ways and become a true pro.. We need to better this industry in the eye of the public by using factory guidelines and proper technique..

charging

Advanced,you
did not give me any idea on what superheat to set for or what subcooling to set for ???????
no one seems to know or you only have a range of super or sub ?
Don't mean to insult or be argumentive, but, in my experience, I find superheat & subcooling to vary too much
to use as a 'definite'

Born,
Piston metering system:
Superheat is variable depending upon the outdoor temp and indoor wetbulb!! That is why I stated that you take the outdoor temp by the outdoor coil and an indoor wetbulb near the return.. Most manufacturer use a slide chart for piston units,,, very simple you look at the chart and line up the outdoor temp and the indoor wetbulb temp on the slide chart and it will give you the superheat(usually allowed (+-)5degrees of that number)... Example:
75 degrees outdoor temp
62 degrees wetbulb temp
on bryant charging chart will give you 15degrees superheat needed +-5degrees...
Example 2:
90 degrees outdoor temp
62 degrees wetbulb temp
on bryant charging chart will give you 5degrees superheat needed +-5degrees..
Example 3(a system that has been down for a while):
90 degrees outdoor temp
76 degrees wetbulb temp(very humid in house)
on bryant charging chart will give you 31degrees superheat needed +-5degrees..
As you can see superheat does vary widely on a system depending on the conditions that the system is operating in..
If a Bryant piston system is properly charged in the first example,, all other situations will properly line up on the chart when those operating parameters happen..

As far as subcool goes,, Most manufactures give you the subcool number on the outdoor unit(i.e. bryant/carrier).. or they give you a graph chart to use based on that number(i.e. Trane) but the chart is based off of the fixed subcool number.. I remember a Bryant 12seer unit that had a 13degrees subcool required and a bryant 11seer that had a 11degress subcool required.. Most subcool readings allow for a +-3degrees of the required reading..

There is a proper way to charge or check a units charge.. To do this properly all techs should calibrate their gages and temperature probes regularly.. Also it is very important to make sure your temperature probe is secured well to the line and well insulated out of direct sunlight..
As long as proper technique and charts are used you will have a properly charged unit..

Please get some training from a supply house on proper charging.. This field is full of hacks,, we need more true professionals!!! From your comments it seems like you want to be a true pro but just don't know any better.. Time to put aside the ignorance and get educated..

Step up to the education plate...
Good day
J
This is my last post on this subject,, if you truely want to do it the correct way, you can research this subject on this site for more information and seak a proper charging technique class from your local supply house..

P.S. If you want addition contribution to this subject by other members, Please post it in the pro's forum as this is our trade and a diyer does not need to see these posts and try to charge their own unit..

There is no quick charing method. Superheat and subcooling are not variable, there is no room for negotiation.

You want a temperature split that works in every case but you're not willing to accept the fact that the latent load is not a sensible temperature. Sorry to say, your split is usless in the charging procedure.

30 over ambient has long since been a thing of the past if ever it was true.

If you want to charge a unit proper you need to take the time to do it right.

Turn the system on and before you even think about hooking gauges up you need to verify several things.
1. Matched equipment (otherwise the charts are worthless) This also included proper sizing technciques.
2. Verify airflow, it needs to be within 10% or less of nominal or the charts are worthless.
3. Clean system. You cannot use a dirty system (coils, filters, blowers etc) and expect to be right.
4. Season. Your methods for charging are different for cooling then they are for heating. For this free tip we'll discuss cooling.
5. Indoor return temperature, you need to know the DB and WB as it enters the coil, not the space temperature in the home.
6. Outdoor ambient temperature, this is the temperature of the air passing through the outdoor coil, not the temperature at the bank up the street.
7. Calibrated and accurate tools. If you suggest you use a laser guided infared temperature probe, this conversation is over. Gauges should be calibrated regularly.
8. Determine whether you are dealing with a fixed oriface or TXV as a metering device. For this example we'll use a TXV.
9. Line length, size and vertical speration. Exceeding or failing to meet the requirements will result in unfavorable performance.

Now you can attach your gauges. The system has to run for a minimum of 15 minutes before you do anything. You also ned to read and document some oeprational temperatures.
1. Liquid line temperature at service valve
2. LL temp leaving outdoor coil manifold.
2. Suction Line temperature at service valve
3. LL temp at indoor coil
4. SL temp at indoor coil
5. Saturation temperature of suction
6. Saturation temperature of liquid
7. Discharge temperature.

Based on your readings above, (note, pressures are irrelevent), you can examine the charging chart and determine the proper subcooling level. Some mfg's offer pressures based on temperatures in their charts to allow for shall we say ignorant (and I say that in the nicest way) technicians.

For arguments sake lets say the chart dictates a 10 degree subcooling requirement. You still need to figure out the superheat to veryify TXV operation. Now you can add or remove refirgerant according to the subcooling chart. after adding or removing a little, you need to allow time for the system to operate and equilibrate as much as 15 minutes. Recheck and readjust again. Wait again. Once you are at the proper subcooling level, all readings need to be reverified and documented. Just because a reading such as indoor LL temperature is not used in the charging chart doesnt mean you can avoid reading it, it tells you whether there is indeed an issue that needs to be dealt with prior to charging.

The techncian can, with this information "see" into the system to determine and verify optimum performance and efficiency

You tell me, are you worth your wages to use a rule of thumb? Frankly, we could train monkeys to do non-technical charging if it worked and they work for much less than most techncians are willing to work for plus they dont need healthcare policies.

Edit: Advance you are right about the training... Apparently you answered while I was typing my response.

Doc,
Most excellant post..
Much more detailed and more to the point than my post..
I need some training in typing out the thought I have in my head...

And I see your point about superheat not being a variable but being a direct relationship to outside parameters..
I stated it was variable as the latent load varies as does the outdoor temp.. lol
I think we have the same concept just two differant explanations..
Now is that Bottle of beer half full or half empty?
Who cares, its time for another round.. Barmaid!!!

Born,
I just noticed in one of your other posts that you teach HVAC...
I hope that you are not teaching them a bunch of rules of thumb that are useless..
Please get more education and seriously think about if you have enough proper hvac knowledge and hvac education to properly teach your student the proper techniques of this trade,, not a bunch of rules of thumbs..
The equipment being made today is getting more and more less tolerable to rules of thumb.. Thus the need for a hvac student to be taught proper basics..

Please,Please... Fill your hvac students heads with proper techniques not rules of thumb.. The best way to do this is for you to get more education in hvac..

I hope you will be stessing to them the need for static pressure readings.. i.e. return static plus supply static equals total external static pressure...Proper uses of magnehelics,, the importance for load calculations..etc..

Please don't teach these students rules of thumb.. You are now a teacher and should be teaching the proper technique...

response to Doc

thank you DOC YOU THE MAN ,THAT'S EXACTLY THE RESPONSE I WAS LOOKING FOR!!!!!!!I'VE BEEN AWAY FROM H.V.A.C& R,I DO NEED TO BRUSH UP BIG TIME,I DO ADDMIT,NO DOUGHT,BUT YOU WILL SEE THE AMOUNT OF KNOW IT ALL'S AND NO FACT'S!!YOU WILL AGREE THEIR IS NO SUCH THING AS A STUPID QUESTION??
THANK'S AGAIN,I SET YOU OUT FROM THE CROWD[MY OPINION]

P.S.I AM LICENSED IN TX[READEM & WEEP]BUT NOT CURRENTLY PRACTICEING,LOOING TO BRUSH UP,TUSHA

Thank you for responses

When considering the entire hvac system, I feel that the purpose of central heat & air is to supply an area ( say a home ) with the right volume of air ( air changes/hr ) at the right temperature. Is this correct ??

And, I ass u me that i can be more efficeient if I either:
1) With a certain movement of air ( cfms ), If I can make the air cooler, then my system is more efficient.
2) If I can increase my air movement ( cfm ), and maintain the same supply air temperature, then I have increased my efficiency.